Water Research
ACCEPTED MANUSCRIPT
MANUSCRIPT
ACCEPTED ACCEPTED MANUSCRIPT
1 Determining the long-term effects of H2S concentration, relative
2 humidity and air temperature on concrete sewer corrosion
3 Guangming Jiang 1, Jurg Keller 1, Philip L. Bond 1,*
4 1. Advanced Water Management Centre, The University of Queensland, St. Lucia,
5 Queensland 4072, Australia
6 * Corresponding author. E-mail: [email protected], Tel.: +61 7 3365 4727; Fax:
7 +61 7 3365 4726.
8 Abstract
9 Many studies of sewer corrosion are performed in accelerated conditions that are not
10 representing the actual corrosion processes. This study investigated the effects of various 11 factors over 3.5 years under controlled conditions MANUSCRIPT simulating the sewer environment. 12 Concrete coupons prepared from precorroded sewers were exposed, both in the gas phase and
13 partially submerged in wastewater, in laboratory controlled corrosion chambers. Over the 45
14 month exposure period, three environmental factors of H2S concentration, relative humidity
15 and air temperature were controlled at different levels in the corrosion chambers. A total of
16 36 exposure conditions were investigated to determine the long term effects of these factors
17 by regular retrieval of concrete coupons for detailed analysis of surface pH, corrosion layer 18 sulfate levels andACCEPTED concrete loss. Corrosion rates were also determined for different exposure 19 periods. It was found that the corrosion rate of both gas-phase and partially-submerged
20 coupons was positively correlated with the H2S concentration in the gas phase. Relative
21 humidity played also a role for the corrosion activity of the gas-phase coupons. However, the
22 partially-submerged coupons were not affected by humidity as the surfaces of these coupons ACCEPTED MANUSCRIPT 23 were saturated due to capillary suction of sewage on the coupon surface. The effect of
24 temperature on corrosion activity varied and possibly the acclimation of corrosion-inducing
25 microbes to temperature mitigated effects of that factor. It was apparent that biological
26 sulfide oxidation was not the limiting step of the overall corrosion process. These findings
27 provide real insights into the long-term effects of these key environmental factors on the
28 sewer corrosion processes.
29 Key words
30 Sewer; corrosion; concrete; hydrogen sulfide; humidity; temperature
31 Nomenclature
32 BET Brunauer–Emmett–Teller
33 GPC Gas-phase concrete coupons MANUSCRIPT 34 MICC Microbially induced concrete corrosion
35 PLC Programmable logic controller
36 PSC Partially-submerged concrete coupons
37 SOB Sulfide-oxidizing bacteria
38 SOR Sulfide oxidation rate
39 RH RelativeACCEPTED humidity
40 RTD Resistance temperature detector
41 ACCEPTED MANUSCRIPT
42 1 Introduction
43 Sewer networks for transport of wastewater (sewage) are among the most important
44 infrastructure elements of modern cities, and their establishment has been achieved through
45 the continuous public investment for more than a century. The total asset value of these
46 networks is estimated to be about one trillion dollars in the USA and $100 billion in Australia
47 (Brongers et al., 2002). However, concrete corrosion is a costly degradation process affecting
48 sewer systems worldwide. Corrosion causes loss of concrete mass and deteriorates the
49 structural capacity, leading to cracking of sewer pipes and ultimately structural collapse. The
50 rehabilitation and replacement of damaged sewers is very costly. In the USA alone, corrosion
51 is causing sewer asset losses estimated at around $14 billion per year (Brongers et al., 2002).
52 This cost is expected to increase as the aging infrastructure continues to fail (Sydney et al.,
53 1996; US EPA, 1991). MANUSCRIPT 54 Concrete corrosion in sewers involves a combination of physical, chemical and biological 55 processes, and is commonly termed microbially induced concrete corrosion (MICC). The
56 fresh concrete surface of sewer pipes after construction is not favorable for microbial growth
57 due to the strongly alkaline nature of concrete. The concrete surface changes to a favorable
58 environment during the initial stages of corrosion by carbonation (by CO2) and H2S
59 acidification (Joseph et al., 2012). In gravity sewers, favorable physicochemical conditions
60 for microbial colonization occur on the concrete surface through adequate water availability 61 (due to elevatedACCEPTED relative humidity), high concentrations of carbon dioxide, high 62 concentrations of H2S and lowered surface pH (Wei et al., 2014).
63 In the sewer network H2S is generated by anaerobic sulfate-reducing bacteria mostly in the
64 rising main (pumped) sections. This H2S is transported to the gravity flow sections of the
65 sewer and is emitted to the gas phase where it is absorbed in the condensation layer of the ACCEPTED MANUSCRIPT
66 exposed pipe surface (sides and crown), followed by the biological oxidation of H2S and the
67 production of sulfuric acid (Parker, 1945a; b; 1947; Pomeroy and Bowlus, 1946), which is
68 responsible for the corrosive attack on the concrete (Islander et al., 1991; Ismail et al., 1993).
69 Recent studies have identified various microorganisms, primarily sulfide-oxidizing bacteria
70 (SOB), involved in this acid production (Cayford et al., 2012; Hernandez et al., 2002; Kelly
71 and Wood, 2000; Nica et al., 2000; Okabe et al., 2007; Santo Domingo et al., 2011).
72 The sewer pipe intact cement (mainly hydrated calcium silicate (CaO⋅⋅ SiO22 2H O ) and
73 portlandite (Ca(OH)2)) reacts with the biologically generated sulfuric acid, to form two
74 important corrosion products: gypsum in the matrix of the corrosion layer and ettringite near
75 the corrosion front with higher pH (Jiang et al., 2014; O'Connell et al., 2010). Both gypsum
76 and ettringite are highly expansive minerals, which are believed to cause internal cracking at
77 the concrete interface and hence enhance the corrosion development (Monteny et al., 2000; 78 Parande et al., 2006). Additionally, Jiang et al. (2014)MANUSCRIPT recently found that micro-cracking in 79 the corroding concrete is likely caused by the continuous cycle of the dissolution of iron salts
80 in the corrosion layer and rust precipitation at the corrosion front.
81 Various technologies are used to alleviate and control corrosion problems in concrete sewers.
82 This includes liquid- and gas-phase technologies that use chemicals such as nitrates or iron
83 salts to reduce the formation/emission of H2S (Gutierrez et al., 2008; Jiang et al., 2011; Jiang
84 et al., 2013; Jiang and Yuan, 2013; Zhang et al., 2009) or remove H2S from sewer air (Sivret 85 and Stuetz, 2010).ACCEPTED Other technologies include construction of new sewers with corrosion- 86 resistant concrete or to repair corroded concrete surfaces with corrosion resistant layers (De
87 Muynck et al., 2009; Haile et al., 2010; Hewayde et al., 2007; Rivera-Garza et al., 2000;
88 Yamanaka et al., 2002; Alexander et al., 2011). ACCEPTED MANUSCRIPT 89 The most direct indicator for the effectiveness of these various technologies should be the
90 corrosion rate, in terms of concrete depth lost over time (mm/year) under sewer conditions.
91 Due to the difficulty to measure actual corrosion rates in operating sewers, the control
92 efficiency is usually evaluated based on the liquid phase sulfide or gaseous H2S
93 concentrations before and after treatment. However, this is only one of the factors related to
94 concrete sewer corrosion. Full understanding of the relationships between the corrosion rate
95 and various sewer environmental factors such as the H2S concentration, relative humidity and
96 temperature are critical to evaluate and optimize the corrosion control strategies.
97 Many laboratory based studies have used accelerated tests or short term experiments of up to
98 6 months exposure to investigate sewer corrosion. These accelerated tests may be performed
99 by exposure of concrete samples to sulfuric acid solutions, and sometimes with heavy inocula
100 of sulfur oxidising bacteria (Herisson et al., 2013; Yousefi et al., 2014), and result in highly 101 enhanced activity that leads to corrosion rates thatMANUSCRIPT may be 10 times higher than those detected 102 in real sewers. Such experiments have been useful for relative comparisons, for example, to
103 test the corrosion of various concrete mixtures, or the effectiveness of sacrificial or
104 permanent coatings. However, these tests are not relevant for ascertaining the conditions and
105 factors that determine concrete corrosion. To date there is a severe lack of studies that
106 investigate these factors in well controlled conditions that simulate the sewer environment
107 and over time scales that are relevant to sewer corrosion.
108 The H2S concentration in real sewers varies greatly due to different hydraulic retention times,
109 flow velocities andACCEPTED wastewater characteristics. In addition to high relative humidity and high
110 atmospheric oxygen content, a H2S level >2 ppm is suggested to be required for the sulfide
111 oxidation to proceed on concrete sewers (O'Dea, 2007). It is thought that the corrosion rate is
112 directly proportional to the H2S emission rate (De Belie et al., 2004). The well-known ACCEPTED MANUSCRIPT 113 Pomeroy model can be used to calculate the deterioration rate of concrete sewer pipes based
114 on equation 1 (Pomeroy, 1990):
11.5kφ 115 C = sw (1) r alk
116 Where Cr = corrosion rate (mm/year); k = factor related to the acid formation, based on
117 climate conditions, 0.8 in moderate climates; φsw= sulfide flux at the air-wall interface [g
2 118 H2S/(m hr)]; and alk = alkalinity of the pipe material (g CaCO3/g concrete).
119 In sewers, water and nutrients provided by sewage are found to promote the microbial
120 corrosion, especially for the area close to the water level in a sewer pipe (Mori et al., 1992).
121 For the pipe surface further away from the water level, the relative humidity of the sewer air
122 and the condensation process on the concrete surface would generate a water film for
123 microbial growth. Previously, it was reported that humidity plays a role in surface 124 neutralization at the early stage of sewer concrete MANUSCRIPT corrosion (Joseph et al., 2012). However, 125 there is a lack of understanding of the specific role humidity plays in the long-term
126 development of sewer concrete corrosion.
127 Short-term changes of temperature are typical for sewer systems and the interactions between
128 sewer systems and receiving water (Vollertsen et al., 1999). One important process for sewer
129 concrete corrosion is the air-water transfer of hydrogen sulfide, which was found to increase
130 with increasing temperature (Yongsiri et al., 2004). It is widely accepted that the sulfide 131 oxidation rate, bothACCEPTED chemically and biologically, increases with temperature, which can be 132 described with the Arrhenius relationship (Nielsen et al., 2004; Nielsen et al., 2006). The
133 sulfide oxidation rate is reported to double for a temperature increase of 7-9 °C. In addition,
134 sewer systems located in different climates may have biological activity that is acclimated to
135 different temperatures. The sulfide oxidation rates, and accordingly corrosion rates, could ACCEPTED MANUSCRIPT 136 thus be very different for different climatic regions. However, no literature has compared the
137 long-term effects of temperature on concrete corrosion.
138 This study aims to enhance the understanding of the correlation between the initiation and
139 development of sewer corrosion and the sewer environmental factors including H2S
140 concentration, relative humidity and temperature. In particular, we aim to determine how the
141 corrosion rates are affected by these key environmental factors. Using precorroded concrete
142 coupons exposed to thirty-six separate conditions in well-controlled laboratory chambers that
143 simulate conditions typically found in various sewers (six levels of H2S concentration, two
144 levels of relative humidity (RH) and three levels of temperature), the change of surface
145 properties and formation of corrosion products were measured. In particular, the mass losses
146 due to corrosion after different exposure times (up to about 3.5 years) were determined using
147 advanced photogrammetry. The results delineate the temporal development of corrosion
148 under different sewer environments. MANUSCRIPT 149 2 Material and Methods
150 2.1 Concrete coupons
151 The coupons were prepared from corroded concrete sewer slabs obtained from Sydney Water
152 Corporation, Australia. Coupon dimensions were approximately 100 mm (length) × 70 mm
153 (width) × 70 mm (thickness). After cutting, the coupons were washed in fresh water to 154 remove any existingACCEPTED corrosion products and surface contamination. Washed coupons were 155 then dried in an oven (Thermotec 2000, Contherm) at 60 °C for 3 days to achieve similar and
156 stable initial water content (Joseph et al., 2010).
157 One of the original surfaces of the coupons, i.e. the internal surface of the pipe, was
158 designated as the surface to be exposed to H2S. After cutting, the coupons were embedded in ACCEPTED MANUSCRIPT 159 stainless steel frames using epoxy (FGI R180 epoxy & H180 hardener) with the steel frame
160 providing a reference point for determining the change in thickness due to corrosion (Jiang et
161 al., 2014). As described in section 2.2, the frame-enclosed coupons were used in the gas-
162 phase exposure. In addition, the same number of concrete coupons without enclosures were
163 partially submerged in real sewage in the corrosion chambers (Figure 1).
164 2.2 Corrosion chamber and exposure condition
165 Thirty-six identical corrosion chambers were constructed to achieve a controlled environment
166 simulating that of real sewers (Table 1). The controlled factors include combinations of three
167 gas-phase temperatures (17 °C, 25 °C and 30 °C), two levels of RH (100% and 90%) and six
168 H2S levels (0 ppm, 5 ppm, 10 ppm, 15 ppm, 25 ppm and 50 ppm). The RH is sensitive to
169 temperature and the low RH (90%) is fluctuating between 85% and 95%. Temperature and
170 H2S variations are within 1 °C and 2 ppm, respectively. MANUSCRIPT 171 (Approximate position of Table 1)
172 The chambers were constructed of glass panels of 4 mm thickness. The dimensions of the
173 chambers were 550 mm (L) × 450 mm (D) × 250 mm (H) (Figure 1). Each chamber
174 contained 2.5 L of domestic sewage that was collected from a local sewer pumping station
175 and replaced every two weeks. Six coupons enclosed in frames were exposed to the gas phase
176 within the chambers with the exposed surface facing downwards approximately 110 mm
177 above the sewage surface (Figure 1). These gas-phase concrete coupons were named as GPC
178 coupons for theACCEPTED purpose of discussion. This coupon arrangement simulated the sewer pipe
179 crown, a location which is reported to be highly susceptible to sulfide induced corrosion
180 (Mori et al., 1992; Vollertsen et al., 2008). Another six bare coupons were placed at the
181 bottom of the chambers, which were thus partially submerged (approx. 20-30 mm) in the
182 wastewater simulating the concrete sewer pipe near the water level, which is also a region of ACCEPTED MANUSCRIPT 183 high corrosion activity. These partially-submerged concrete coupons were named as PSC
184 coupons for the purpose of discussion.
185 (Approximate position of Fig. 1)
186 To achieve the specified H2S gaseous concentrations in the corrosion chamber, Na2S solution
187 was injected into a container partially filled with acid (13% HCl), using a corrosion-resistant
188 solenoid pump (Bio-chem Fluidics, model: 120SP2440-4TV) with a dispense volume of 40
189 µL. The H2S concentrations were monitored using a H2S gas detector (OdaLog Type 2) with
190 a range between 0 and 200 ppm (App-Tek International Pty Ltd, Brendale, Australia). To
191 ensure the proper operation of the H2S sensor, it was replaced with a spare H2S sensor weekly.
192 The used one was then regenerated in a desiccator chamber with silica gel beads. The H2S
193 gas sensors were routinely calibrated and serviced by the supplier every six months. A
194 programmable logic controller (PLC) was employed to monitor the H2S concentration and to 195 trigger the dosing pump for Na2S addition to MANUSCRIPT maintain the specified H2S concentrations 196 (Figure 1).
197 The corrosion chambers were installed in three cabinets, i.e. A, B and C (12 chambers each
198 cabinet), with different sewage temperatures controlled by re-circulating temperature
199 controlled water through glass tubes immersed in the sewage. The relative humidity was thus
200 controlled at approximately 100% or 90% for different chambers. Humidity was monitored
201 using two resistance temperature detector (RTD) probes, of which one acts as wet and 202 another acts asACCEPTED dry bulb inside the chamber. Another of these probes was employed to 203 monitor the sewage temperature.
204 2.3 Long-term monitoring of corrosion development ACCEPTED MANUSCRIPT 205 The corrosion chambers were operated for up to 45 months since December 2009. The
206 environmental factors were checked daily to ensure proper operation of the chambers. As
207 shown in the typical daily profiles of H2S concentration, gas temperature and relative
208 humidity (Fig. SI-1), the corrosion chambers were well maintained at the designated
209 conditions.
210 Periodically, at intervals between 6-10 months, one set of coupons (one gas-phase coupon
211 and one partially-submerged coupon) were retrieved from each corrosion chamber for
212 detailed analysis. A standard step-by-step procedure of methods has been employed to
213 measure surface pH, followed by sampling for sulfur species and then photogrammetry
214 analysis (thickness change).
215 2.4 Corrosion sampling and analysis
216 A flat surface pH electrode (Extech PH150-C concretMANUSCRIPTe pH kit, Extech Instruments, USA) was 217 used to measure the coupon surface pH. The pH meter was allowed to reach steady reading
218 after contacting the electrode with the measuring spots wetted by about 1 mL of milliQ water.
219 Four measurements were made on randomly selected spots on the coupon surface to
220 determine an average value.
221 After measuring the surface pH, the exposed surface of concrete coupons was washed using a
222 high pressure washer (Karcher K 5.20 M). Four liter of water was used for each coupon. The
223 wash-off water was homogenized using a magnetic mixer for 2 hours before subsamples
224 taken into sulfideACCEPTED anti-oxidant buffer solution (Keller-Lehmann et al., 2006). A Dionex ICS-
225 2000 IC with an AD25 absorbance (230 nm) and a DS6 heated conductivity detector (35 ºC)
226 was used to measure the soluble sulfur species. ACCEPTED MANUSCRIPT 227 Five photos for each coupon were taken to measure the coupon thickness after washing using
228 photogrammetry (Wells et al., 2009). A 3D image of the exposed surface for each coupon
229 was generated to calculate the surface height of the coupon relative to the stainless steel
230 frame as the reference plane. The decrease in thickness after certain exposure time was then
231 calculated by subtracting the average thickness after washing from the average thickness
232 before exposure. This technique not only enables an accurate change in coupon thickness to
233 be determined irrespective of the surface roughness but also provides a detailed record of the
234 spatial distribution of the losses that occurred.
235 2.5 Data analysis
236 As the concrete coupons used in the study were previously corroded, the initial corrosion
237 rates, i.e. the first year, may be different from the long-term rates during later stages.
238 Different corrosion rates were thus calculated separately using the corrosion loss (i.e. 239 decrease of average coupon depth) data for exposure MANUSCRIPT times between 0-12, 12-24, and 24-35 240 months, respectively. The estimated corrosion rates were subsequently analyzed to identify
241 the controlling environmental factors of the corrosion processes.
242 First, regression tree models (R ver 3.03, http://www.R-project.org/) were used to find out
243 which of the three environmental factors were important (exploratory analysis). Tree models
244 were used as they can give a clear picture of the structure in the data and they can
245 automatically accommodate complex interactions between explanatory variables. Recursive
246 partitioning, thatACCEPTED successively splits the data by the explanatory variables (i.e. H2S 247 concentration, relative humidity and gas temperature), was used to distinguish groupings in
248 the corrosion rates. To further investigate the importance of each environmental factor for the
249 corrosion rates at different corrosion stages, statistic models with all three factors were ACCEPTED MANUSCRIPT 250 analyzed using analysis of variance in R. These maximal models were then simplified by
251 backward selection to get minimal adequate models (MAM).
252 3 Results and Discussion
253 3.1 Surface pH
254 It was seen that the surface pH of the GPC coupon exposed to 0 ppm H2S stayed around the
255 original level of 8 for both humidity levels (Figure 2). Similarly, the PSC coupons exposed to
256 0 ppm H2S, had surface pH remaining around initial levels of 7-8 at both humidity levels.
257 Initial pH of fresh concrete is usually 11-12, which can be reduced to around 10 by
258 carbonation. Further lowering of the surface pH occurs partially by H2S itself and then more
259 substantially by the sulfuric acid produced by biological oxidation of H2S (Joseph et al.,
260 2012). Consequently, these precorroded concrete coupons had reached reduced pH levels, 261 indicating that they had experienced corrosion atta MANUSCRIPTck by sulfuric acid. 262 (Approximate position of Fig. 2)
263 The starting pH around 8 implies that the concrete surface was already suitable for the growth
264 of neutrophilc sulfide-oxidizing bacteria (Islander et al., 1991). For GPC concrete coupons at
265 100% RH, all coupons reached about pH 4 after 12 months of exposure. At this acidic pH the
266 concrete was suitable for the succession of acidophilic sulfide-oxidizing bacteria. Higher
267 levels of H2S achieved faster reduction of surface pH (Figure 2). It is evident that GPC 268 coupons exposedACCEPTED to 50 ppm reached pH 4 after 6 months exposure while the surface pH of 269 other H2S levels more or less achieved the same pH after longer exposure time. For GPC
270 coupons at 90% RH, the surface pH reduction was 1-2 unit less compared to 100% RH in
271 many instances. This implies that humidity levels are crucial for the pH reduction, which is ACCEPTED MANUSCRIPT 272 mainly due to the biological sulfide oxidation. No clear effects of temperature on surface pH
273 of GPC coupons could be visually determined from the data.
274 The surface pH of nearly all PSC coupons exposed to H2S gas experienced a first sharp drop
275 at 6 months of exposure, reaching a relatively steady value of pH 3-4 (Figure 2). This
276 suggests that corrosion-inducing acidophilic microorganisms were established on these
277 coupons within a few months after being placed into the corrosion chambers. Likely the
278 wastewater provides sufficient moisture, nutrients and inoculum for the succession of
279 corrosion biofilms. These coupons then experienced another drop in surface pH after
280 remaining semi-steady up to around 25-26 months exposure. After 34 months exposure, a
281 surface pH around 2 was achieved on coupons exposed to 15-50 ppm. The data did not reveal
282 any difference of surface pH among the two different RH levels and the three temperature
283 levels. Overall, all coupons surface pH was lowered to similar levels to between pH 2 to 4, as 284 long as some level of H2S gas was present. MANUSCRIPT 285 3.2 Sulfate concentrations on corroding concrete surface
286 Significant levels of surface sulfate were measured on the GPC coupons (Figure 3). These
287 generally slightly increased with gas phase H2S levels, and also with the exposure time. At
288 100% RH, slightly more sulfate, around 50-100 gS/m2, was formed in comparison to coupons
289 at 90% RH for all H2S levels. This implies that GPC coupons with higher moisture content
290 experienced increased biological H2S oxidation and sulfate production. No clear effects of 291 temperature on theACCEPTED sulfate concentration were detected. 292 (Approximate position of Fig. 3)
293 Corrosion layer sulfate levels of the PSC coupons exposed to 0 ppm H2S were detected to be
294 very stable throughout the exposure time, i.e. at about 50 g S/m2 (Figure 3). This sulfate
295 basically originates from the pre-exposure as real sewer pipe before being placed into the ACCEPTED MANUSCRIPT 296 corrosion chambers. Sulfate levels on the PSC coupons increased with increasing gas phase
297 H2S levels and exposure time.
298 No clear effects of temperature on sulfate were found for the different conditions. It is clear
299 that the sulfate concentration on the PSC coupons was about 2-3 times higher than that
300 measured on the surface of the GPC coupons. No significant difference was detected for the
301 PSC coupons at the two relative humidity levels. This is reasonable considering the PSC
302 coupons were partially submerged in wastewater, which would effectively saturate much of
303 the exposed surface of these coupons though capillary draw up of water from the wastewater.
304 3.3 Corrosion losses of concrete coupons
305 About 2 mm of corrosion loss (thickness decrease) was detected for nearly all coupons
306 exposed to 0 ppm H2S (Figure 4). This corrosion loss is likely due to previous corrosion 307 before being placed into the corrosion chamber.MANUSCRIPT Although the loose corrosion layer was 308 removed during the coupon preparation, it appears that an additional residual corrosion layer
309 remained on the coupon surface and was mobilized during the 4 years of exposure in the
310 highly humid chambers. Likely, this mobilization also caused the high levels of sulfate
311 detected on the 0 ppm coupons, i.e. 50-100 gS/m2 (Figure 3).
312 In the presence of H2S, the corrosion loss was around 2-8 mm for GPC coupons at 100% RH,
313 with some cases reaching 6-8 mm at high H2S concentrations (10-50 ppm) (Figure 4). For
314 coupons under 90% RH, the corrosion loss was around 2-4 mm for 5-15 ppm of H2S, and
315 around 4-6 mmACCEPTED for 25-50 ppm of H2S. A clear increasing trend of corrosion loss with
316 exposure time was observed. This trend was approximately linear for all H2S levels except
317 some fluctuations were observed at 5 ppm H2S. No clear effects of gas temperature on the
318 corrosion losses were found for the different conditions. ACCEPTED MANUSCRIPT 319 (Approximate position of Fig. 4)
320 The PSC coupons exposed to 0 ppm H2S show corrosion losses of around 2 mm, similar to
321 the GPC coupons, and this was consistent throughout the exposure period. PSC coupons
322 exposed to 5-50 ppm of H2S showed higher corrosion losses, ranging from 3 mm at 5 ppm of
323 H2S to 15 mm at 25 and 50 ppm of H2S. In comparison to GPC coupons, the corrosion loss
324 was about 1-2 times higher for the same exposure conditions (Figure 4). This could be
325 explained in that the PSC coupons continuously obtained nutrients and moisture from the
326 wastewater, and this led to more active biological acid generation and corrosion.
327 For PSC coupons exposed to high H2S at 25 ppm (90% RH) and 50 ppm (both 90% and 100%
328 RH), very high corrosion loss was detected at 12-18 months while similar or lower values
329 were measured in later analysis. This could possibly be due to the corrosion layer periodically
330 providing a protective barrier that lowered corrosion activity. This occurred especially when 331 the corrosion loss was >10 mm, this suggesting MANUSCRIPT a corrosion layer of 20-40 mm thickness 332 when considering the expansive nature of gypsum and ettringite. A thick corrosion layer
333 could retard the diffusion of sulfuric acid through this layer to the intact concrete core.
334 Consequently, it is apparent that diffusion is the limiting factor of the corrosion process.
335 Although it is suggested that biogenic corrosion tends to occur throughout the whole
336 corrosion layer (Monteny et al., 2000), other reports indicate that SOB mainly reside in the
337 outer parts (1.5 mm) of the corrosion layer due to transport limitations of H2S and oxygen
338 (Okabe et al., 2007). ACCEPTED 339 3.4 Concrete coupon corrosion rate
340 Corrosion rates were determined over three time periods within the 45 month exposure for
341 the GPC and the PSC coupons (Figures 5 and 6). For the GPC coupons the corrosion rates in
-1 342 the first 12 months were more or less similar at 2-3 mm year for the different H2S ACCEPTED MANUSCRIPT 343 concentrations (Figure 5) (significance p-value p=0.6, Table SI-1). However, trends of
344 increasing corrosion rates were evident with increasing H2S levels during the latter two
345 exposure periods (Figure 5), implicating the importance of this factor on corrosion rates. Also,
346 there seems to be a clear difference between the two levels of relative humidity (p=0.03) with
347 higher corrosion rates at the higher humidity. In contrast the effects of gas temperature on
348 corrosion rates were not evident (p=0.7). It was seen that initial corrosion rates were higher
349 than those measured during the latter exposure periods of 12-24 and 24-45 months. These
350 apparent high rates may be due to loss of previously corroded residual layers (as mentioned
351 in section 3.3).
352 (Approximate position of Fig. 5)
353 Due to the possible interference of a residual corrosion layer, the long-term and stable
354 concrete corrosion rates are likely better detected for the 12-24 and 24-45 month exposure 355 periods (rows 2 and 3 in Figure 5). There is a clea MANUSCRIPTr increasing trend of these corrosion rates 356 with the increase of H2S concentration. Tree analysis (Figure SI-1) indicated this and the
357 ANOVA analysis confirmed this observation with p values of 0.003 and 0.002 for the two
358 exposure periods respectively. Also, relative humidity was again shown to be a significant
359 factor affecting the corrosion rates, with p values of 0.03 and 0.01 for 12-24 and 24-45
360 months respectively. As found for corrosion losses, the gas temperature was not a significant
361 factor for corrosion rates (p=0.6 and 0.8). Although it is expected that higher temperature
362 would stimulate biological activity, this effect may not be noticeable due to the corrosion rate
363 limitations causedACCEPTED by either the H2S availability or the RH. Previously, no clear effects of
364 temperature (5-17 °C) were also found for the hydrogen sulfide oxidation kinetics (Nielsen et
365 al., 2012). This was attributed to the population dynamics of SOB in the corrosion layers.
366 (Approximate position of Fig. 6) ACCEPTED MANUSCRIPT 367 Corrosion rates were determined for the concrete coupons partially submerged in wastewater
368 (Figure 6). It is noticeable that for both the initial corrosion rate (0-12 months) and the long-
369 term corrosion rates (12-24 and 24-45 months), the increasing trend with increasing H2S
370 concentration is evident, with respective p-values of 8.6×10-5, 1.5×10-6, and 6.4×10-7. This
371 confirms that H2S is a key controlling factor of the corrosion rates over periods of long term
372 exposure in sewer conditions. For the PSC coupons the other two factors were not significant.
373 This is understandable as these coupons were partially submerged and thus humidity would
374 not play such a role on the water content in the corrosion layer. It can be concluded that the
375 corrosion rate for PSC coupons was primarily controlled by the H2S concentrations. The
376 same applies to the GPC coupons, although humidity also plays a significant role to provide
377 moisture content at the GPC coupon surface via vapor condensation.
378 For the GPC and PSC coupons, minimum adequate models (MAM) were identified through 379 the backward selection processes which drop oneMANUSCRIPT explanatory factor for the corrosion rate 380 each time. MAM for GPC includes both H2S concentration and relative humidity while the
381 MAM for PSC only requires H2S concentration. Theoretically the corrosion rate is directly
382 proportional to the sulfide oxidation rate (SOR), which is related to gaseous H2S
383 concentration in a power function (Jensen et al., 2009; Vollertsen et al., 2008). The
384 relationship between the SOR and relative humidity is not that well defined. It is assumed
385 that the SOR is proportional to the water content in the concrete because water is essential for
386 possible biological and chemical reactions. The water content can be estimated from the 387 relative humidityACCEPTED using a Brunauer–Emmett–Teller (BET) sorption isotherm (Xi et al., 1994) . 388 Based on these considerations and the statistical analysis, the following models were
389 proposed to estimate corrosion rates.
390 PSC: CkC= ⋅ n + C (2) rHSri2 ACCEPTED MANUSCRIPT
391 GPC: CkC= ⋅⋅n f() RHC+ (3) rHSBETri2
-1 392 Where Cr is the corrosion rate (mm year ); C is the gaseous H2S concentration; k and n HS2
393 are model constants to be estimated from the experimental data. Cri represents the corrosion
394 caused due to previous exposure. fRHBET () is a BET sorption isotherm. For the GPC model,
395 only two levels of relative humidity have been examined in the experiments, making it
396 impossible to validate this model. However, the PSC model was examined by curve fitting
397 with the experimental data (Figure 7). It adequately described the relationship between
398 corrosion rates and H2S concentrations.
399 (Approximate position of Fig. 7)
400 In real sewers, the H2S concentration shows high variation due to the sewage flow dynamics
401 and fluctuations of other environmental factors. When estimating the corrosion rate of sewer 402 systems, one possible way is to use the average HMANUSCRIPT2S concentration in aforementioned models. 403 However, it must be recognized that the sulfide uptake rate, as an indicator of corrosion rate,
404 is not directly proportional to the H2S concentration (Sun et al., 2014). In addition, the H2S
405 concentration in the sewer atmosphere is determined by the balance between H2S release
406 from the wastewater and H2S absorption by the corroding concrete, assuming negligible loss
407 of H2S to the atmosphere. The biological sulfide oxidation in the corrosion biofilms might
408 also be affected by the H2S fluctuation, in terms of the microbial community, its activity and
409 final products of sulfide oxidation. Further research is needed to delineate the corrosion rate
410 in sewers with fluctuatingACCEPTED H2S concentration.
411 4 Conclusions ACCEPTED MANUSCRIPT 412 The importance of environmental factors that may contribute to the corrosion of concrete
413 sewers was evaluated through long-term exposure tests in corrosion chambers simulating real
414 sewers. This has led to the following key findings:
415 • Surface pH on concrete coupons was reduced by 3-4 units within months,
416 suggesting a rapid (re-)establishment of corrosion biofilms. This led to significant
417 sulfate levels detected in corrosion layers on concrete coupons, with concentrations
418 of partially-submerged coupons twice as high as that of coupons located in the gas
419 phase, for the same level of H2S exposure.
420 • After 3.5 years of exposure to H2S, corrosion loss on coupons located in the gas-
421 phase was limited to 2-8 mm and 100% RH coupons lost 1-2 mm more than
422 coupons exposed to 90% RH. In contrast, the partially-submerged coupons showed
423 much higher levels of corrosion, i.e. between 3-15 mm after 45 months exposure.
424 • H2S is a key factor determining the concreteMANUSCRIPT corrosion rates during long-term 425 exposure to sewer conditions. High relative humidity led to increased corrosion rates
426 on coupons located in the gas-phase, but did not affect the rate of the coupons
427 partially submerged in wastewater. No clear effects of temperature were observed
428 for surface pH, sulfate and corrosion loss.
429 • Two models to predict corrosion rates were established and validated for concrete at
430 the sewer crown and for concrete in the vicinity of the wastewater level in the sewer.
431 AcknowledgementsACCEPTED
432 The authors acknowledge the financial support provided by the Australian Research Council
433 and many members of the Australian water industry through LP0882016 the Sewer Corrosion
434 and Odour Research (SCORe) Project (www.score.org.au). ACCEPTED MANUSCRIPT
435 References
436 Alexander, M. G., Fourie, C. (2011) Performance of sewer pipe concrete mixtures with 437 portland and calcium aluminate cements subject to mineral and biogenic acid attack. 438 Materials and Structures 44(1), 313-330. 439 Brongers, M.P.H., Virmani, P.Y. and Payer, J.H. (2002) Drinking Water and Sewer Systems 440 in Corrosion Costs and Preventative Strategies in the United States, United States Department 441 of Transportation Federal Highway Administration. 442 Cayford, B.I., Dennis, P.G., Keller, J., Tyson, G.W. and Bond, P.L. (2012) High-throughput 443 amplicon sequencing reveals distinct communities within a corroding concrete sewer system. 444 Applied and Environmental Microbiology 78(19), 7160-7162. 445 De Belie, N., Monteny, J., Beeldens, A., Vincke, E., Van Gemert, D. and Verstraete, W. 446 (2004) Experimental research and prediction of the effect of chemical and biogenic sulfuric 447 acid on different types of commercially produced concrete sewer pipes. Cement and Concrete 448 Research 34(12), 2223-2236. 449 De Muynck, W., De Belie, N. and Verstraete, W. (2009) Effectiveness of admixtures, surface 450 treatments and antimicrobial compounds against biogenic sulfuric acid corrosion of concrete. 451 Cement and Concrete Composites 31(3), 163-170. 452 Gutierrez, O., Mohanakrishnan, J., Sharma, K.R., Meyer, R.L., Keller, J. and Yuan, Z. (2008) 453 Evaluation of oxygen injection as a means of controlling sulfide production in a sewer system. 454 Water Research 42(17), 4549-4561. 455 Haile, T., Nakhla, G., Allouche, E. and Vaidya, S. (2010) Evaluation of the bactericidal 456 characteristics of nano-copper oxide or functionalized zeolite coating for bio-corrosion 457 control in concrete sewer pipes. Corrosion Science MANUSCRIPT 52(1), 45-53. 458 Herisson, J., van Hullebusch, E.D., Moletta-Denat, M., Taquet, P. and Chaussadent, T. (2013) 459 Toward an accelerated biodeterioration test to understand the behavior of Portland and 460 calcium aluminate cementitious materials in sewer networks. International Biodeterioration & 461 Biodegradation 84, 236-243. 462 Hernandez, M., Marchand, E.A., Roberts, D. and Peccia, J. (2002) In situ assessment of 463 active Thiobacillus species in corroding concrete sewers using fluorescent RNA probes. 464 International Biodeterioration & Biodegradation 49(4), 271-276. 465 Hewayde, E.H., Nakhla, G.F., Allouche, E.N. and Mohan, P.K. (2007) Beneficial impact of 466 coatings on biological generation of sulfide in concrete sewer pipes. Structure and 467 Infrastructure Engineering 3(3), 267 - 277. 468 Islander, R.L., Devinny, J.S., Mansfeld, F., Postyn, A. and Shih, H. (1991) Microbial Ecology 469 of Crown Corrosion in Sewers. Journal of Environmental Engineering 117(6), 751-770. 470 Ismail, N., Nonaka,ACCEPTED T., Noda, S. and Mori, T. (1993) Effects of carbonation on microbial 471 corrosion of concretes. Journal of Construction Management & Engineering 20(474), 11-138. 472 Jensen, H.S., Nielsen, A.H., Hvitved-Jacobsen, T. and Vollertsen, J. (2009) Modeling of 473 Hydrogen Sulfide Oxidation in Concrete Corrosion Products from Sewer Pipes. Water 474 Environment Research 81(4), 365-373. 475 Jiang, G., Gutierrez, O., Sharma, K.R., Keller, J. and Yuan, Z. (2011) Optimization of 476 intermittent, simultaneous dosage of nitrite and hydrochloric acid to control sulfide and 477 methane production in sewers. Water Research 45(18), 6163-6172. ACCEPTED MANUSCRIPT 478 Jiang, G., Sharma, K.R. and Yuan, Z. (2013) Effects of nitrate dosing on methanogenic 479 activity in a sulfide-producing sewer biofilm reactor. Water Research 47(5), 1783-1792. 480 Jiang, G., Wightman, E., Donose, B.C., Yuan, Z., Bond, P.L. and Keller, J. (2014) The role of 481 iron in sulfide induced corrosion of sewer concrete. Water Research 49(0), 166-174. 482 Jiang, G. and Yuan, Z. (2013) Synergistic inactivation of anaerobic wastewater biofilm by 483 free nitrous acid and hydrogen peroxide. Journal of Hazardous Materials 250–251, 91-98. 484 Joseph, A.P., Bond, P. and Keller, J. (2010) Examination of concrete corrosion using a 485 laboratory experimental set up simulating sewer conditions. In: 6th IWA Specialist 486 Conference on Sewer Processes and Networks, 7-10 November 2010, Surfers Paradise, Gold 487 Coast, Australia. 488 Joseph, A.P., Keller, J., Bustamante, H. and Bond, P.L. (2012) Surface neutralization and 489 H2S oxidation at early stages of sewer corrosion: Influence of temperature, relative humidity 490 and H2S concentration. Water Research 46(13), 4235-4245. 491 Keller-Lehmann, B., Corrie, S., Ravn, R., Yuan, Z. and Keller, J. (2006) Preservation and 492 simultaneous analysis of relevant soluble sulfur species in sewage samples. In: Proceedings 493 of the Second International IWA Conference on Sewer Operation and Maintenance, Vienna, 494 Austria. 495 Kelly, D.P. and Wood, A.P. (2000) Reclassification of some species of Thiobacillus to the 496 newly designated genera Acidithiobacillus gen. nov., Halothiobacillus gen. nov and 497 Thermithiobacillus gen. nov. International Journal of Systematic and Evolutionary 498 Microbiology 50, 511-516. 499 Monteny, J., Vincke, E., Beeldens, A., De Belie, N., Taerwe, L., Van Gemert, D. and 500 Verstraete, W. (2000) Chemical, microbiological, and in situ test methods for biogenic 501 sulfuric acid corrosion of concrete. Cement and Con MANUSCRIPTcrete Research 30(4), 623-634. 502 Mori, T., Nonaka, T., Tazaki, K., Koga, M., Hikosaka, Y. and Noda, S. (1992) Interactions of 503 nutrients, moisture and pH on microbial corrosion of concrete sewer pipes. Water Research 504 26(1), 29-37. 505 Nica, D., Davis, J.L., Kirby, L., Zuo, G. and Roberts, D.J. (2000) Isolation and 506 characterization of microorganisms involved in the biodeterioration of concrete in sewers. 507 International Biodeterioration & Biodegradation 46(1), 61-68. 508 Nielsen, A.H., Hvitved-Jacobsen, T. and Vollertsen, J. (2012) Effect of Sewer Headspace 509 Air-Flow on Hydrogen Sulfide Removal by Corroding Concrete Surfaces. Water 510 Environment Research 84(3), 265-273. 511 Nielsen, A.H., Vollertsen, J. and Hvitved-Jacobsen, T. (2004) Chemical sulfide oxidation of 512 wastewater - effects of pH and temperature. Water Science and Technology 50(4), 185-192. 513 Nielsen, A.H., Vollertsen, J. and Hvitved-Jacobsen, T. (2006) Kinetics and stoichiometry of 514 aerobic sulfide ACCEPTED oxidation in wastewater from sewers-effects of pH and temperature. Water 515 Environment Research 78(3), 275-283. 516 O'Connell, M., McNally, C. and Richardson, M.G. (2010) Biochemical attack on concrete in 517 wastewater applications: A state of the art review. Cement & Concrete Composites 32(7), 518 479-485. 519 O'Dea, V. (2007) Understanding biogenic sulfide corrosion. Materials Performance 46(11), 520 36-39. ACCEPTED MANUSCRIPT 521 Okabe, S., Odagiri, M., Ito, T. and Satoh, H. (2007) Succession of sulfur-oxidizing bacteria in 522 the microbial community on corroding concrete in sewer systems. Applied and 523 Environmental Microbiology 73(3), 971-980. 524 Parande, A.K., Ramsamy, P.L., Ethirajan, S., Rao, C.R.K. and Palanisamy, N. (2006) 525 Deterioration of reinforced concrete in sewer environments. Proceedings of the Institution of 526 Civil Engineers-Municipal Engineer 159(1), 11-20. 527 Parker, D. (1945a) The corrosion of concrete. 2. The fuction of Thiobacillus concretivorus 528 (Nov-spec) in the corrosion of concrete exposed to atmospheres containing hydrogen sulfide. 529 Australian Journal of Experimental Biology and Medical Science 23(2), 91-98. 530 Parker, D. (1945b) The corrosion of concrete. I. The isolation of a species of bacterium 531 associated with the corrosion of concrete exposed to atmospheres containing hydrogen 532 sulphide. Australian Journal of Experimental Biology and Medical Science 23, 81-90. 533 Parker, D. (1947) Species of sulphur bacteria associated with the corrosion of concrete. 534 Nature (London) 159(439). 535 Pomeroy, R. and Bowlus, F.D. (1946) Progress Report on Sulfide Control Research. Sewage 536 Works Journal 18(4), 597-640. 537 Pomeroy, R.D. (1990) The Problem of Hydrogen Sulphide in Sewers, Clay Pipe 538 Development Association Limited, London. 539 Rivera-Garza, M., Olguı́n, M.T., Garcı́a-Sosa, I., Alcántara, D. and Rodrı́guez-Fuentes, G. 540 (2000) Silver supported on natural Mexican zeolite as an antibacterial material. Microporous 541 and Mesoporous Materials 39(3), 431-444. 542 Santo Domingo, J.W., Revetta, R.P., Iker, B., Gomez-Alvarez, V., Garcia, J., Sullivan, J. and 543 Weast, J. (2011) Molecular survey of concreteMANUSCRIPT sewer biofilm microbial communities. 544 Biofouling 27(9), 993-1001. 545 Sivret, E. and Stuetz, R. (2010) Sewer odour abatement practices - An Australian survey. 546 Water 37(7), 77-81. 547 Sun, X., Jiang, G., Bond, P. L., Wells, T., and Keller, J. (2014) A rapid, non-destructive 548 methodology to monitor activity of sulfide-induced corrosion of concrete based on H2S 549 uptake rate. Water Research, 59(1), 229-238 550 Sydney, R., Esfandi, E. and Surapaneni, S. (1996) Control concrete sewer corrosion via the 551 crown spray process. Water Environment Research 68(3), 338-347. 552 US EPA (1991) Hydrogen sulphide corrosion in wastewater collection and treatment system 553 (Technical Report). 554 Vollertsen, J., Almeida, M.d.C. and Hvitved-Jacobsen, T. (1999) Effects of temperature and 555 dissolved oxygen on hydrolysis of sewer solids. Water Research 33(14), 3119-3126. 556 Vollertsen, J., Nielsen,ACCEPTED A.H., Jensen, H.S., Wium-Andersen, T. and Hvitved-Jacobsen, T. 557 (2008) Corrosion of concrete sewers-The kinetics of hydrogen sulfide oxidation. Science of 558 the Total Environment 394(1), 162-170. 559 Wei, S., Jiang, Z., Liu, H., Zhou, D. and Sanchez-Silva, M. (2014) Microbiologically induced 560 deterioration of concrete: a review. Brazilian Journal of Microbiology (ahead), 0-0. 561 Wells, T., Melchers, R.E. and Bond, P. (2009) Factors involved in the long term corrosion of 562 concrete sewers. In: Australasian Corrosion Association Proceedings of Corrosion and ACCEPTED MANUSCRIPT 563 Prevention 2009, Corrosion & Prevention - 2009, 15-18 November 2009, Coffs Harbour, 564 Australia. 565 Xi, Y., Bažant, Z.P. and Jennings, H.M. (1994) Moisture diffusion in cementitious materials 566 Adsorption isotherms. Advanced Cement Based Materials 1(6), 248-257. 567 Yamanaka, T., Aso, I., Togashi, S., Tanigawa, M., Shoji, K., Watanabe, T., Watanabe, N., 568 Maki, K. and Suzuki, H. (2002) Corrosion by bacteria of concrete in sewerage systems and 569 inhibitory effects of formates on their growth. Water Research 36(10), 2636-2642. 570 Yongsiri, C., Vollertsen, J. and Hvitved-Jacobsen, T. (2004) Effect of temperature on air- 571 water transfer of hydrogen sulfide. Journal of Environmental Engineering-Asce 130(1), 104- 572 109. 573 Yousefi, A., Allahverdi, A. and Hejazi, P. (2014) Accelerated biodegradation of cured 574 cement paste by Thiobacillus species under simulation condition. International 575 Biodeterioration & Biodegradation 86, 317-326. 576 Zhang, L., Keller, J. and Yuan, Z. (2009) Inhibition of sulfate-reducing and methanogenic 577 activities of anaerobic sewer biofilms by ferric iron dosing. Water Research 43(17), 4123- 578 4132. 579 580
581 MANUSCRIPT
ACCEPTED ACCEPTED MANUSCRIPT
582 List of Figures
583
584 Figure 1. Side view of the corrosion chamber with H2S concentration, relative humidity and
585 gas temperature controlled by PLC. The orientation of the gas-phase (GPC) and partially-
586 submerged (PSC) coupons is shown.
587 Figure 2. Surface pH of precorroded concrete coupons exposed to different H2S
588 concentrations in corrosion chambers for 45 months. Plots in columns 1 & 2 and columns 3
589 & 4 are for coupons located in the gas-phase and those partially-submerged in sewage,
590 respectively. Filled and empty symbols are for 100% and 90% relative humidity respectively.
591 Figure 3. Sulfate measured on the surface of precorroded concrete coupons exposed to
592 different H2S levels in the corrosion chambers for 45 months. Plots in columns 1 & 2 and
593 columns 3 & 4 are for coupons located in the gas-phase and those partially-submerged in 594 sewage, respectively. Filled and empty symbols MANUSCRIPT are for 100% and 90% relative humidity 595 respectively.
596 Figure 4. Corrosion losses of precorroded concrete coupons exposed to different H2S
597 concentrations in corrosion chambers for 45 months. Plots in columns 1 & 2 and columns 3
598 & 4 are for coupons located in the gas-phase and those partially-submerged in sewage,
599 respectively. Filled and empty symbols are for 100% and 90% relative humidity respectively.
600 Figure 5. Box-plots of corrosion rates of gas-phase concrete coupons related to H2S 601 concentration, relativeACCEPTED humidity and gas temperature in the corrosion chambers. Plots in the 602 three rows are for corrosion rates during 0-12, 12-24, and 24-45 months, respectively.
603 Figure 6. Box-plots of corrosion rates of partially-submerged concrete coupons related to
604 H2S concentration, relative humidity and gas temperature in the corrosion chambers. Plots in
605 the three rows are for corrosion rates during 0-12, 12-24, and 24-45 months, respectively. ACCEPTED MANUSCRIPT 606 Figure 7. Corrosion rates of partially-submerged concrete coupons fitted with the PSC model
607 for 0-12 (A), 12-24 (B), and 24-45 (C) months. Error bars are standard deviations of
608 corrosion rates (•••) determined for the same level of H2S.
609
MANUSCRIPT
ACCEPTED ACCEPTED MANUSCRIPT
Table 1. Controlled environmental factors for the 36 corrosion chambers.
Group [Gas temperature (°C)] A [17 °C] B [25 °C] C [30 °C]
Chamber No. RH (%) H2S (ppmv) RH (%) H2S (ppmv) RH (%) H2S (ppmv) 1 90 0 90 0 90 0 2 100 0 100 0 100 0 3 90 5 90 5 90 5 4 100 5 100 5 100 5 5 90 10 90 10 90 10 6 100 10 100 10 100 10 7 90 15 90 15 90 15 8 100 15 100 15 100 15 9 90 25 90 25 90 25 10 100 25 100 25 100 25 11 90 50 90 50 90 50 12 100 50 100 50 100 50
MANUSCRIPT
ACCEPTED ACCEPTED MANUSCRIPT
MANUSCRIPT
ACCEPTED ACCEPTED MANUSCRIPT
MANUSCRIPT
ACCEPTED ACCEPTED MANUSCRIPT
MANUSCRIPT
ACCEPTED ACCEPTED MANUSCRIPT
MANUSCRIPT
ACCEPTED ACCEPTED MANUSCRIPT
MANUSCRIPT
ACCEPTED ACCEPTED MANUSCRIPT
MANUSCRIPT
ACCEPTED ACCEPTED MANUSCRIPT
MANUSCRIPT
ACCEPTED
ACCEPTED MANUSCRIPT Highlights
• A long-term study (3.5 years) of H2S induced sewer corrosion
• Corrosion rate was positively correlated with gaseous H2S concentration
• High relative humidity led to increased sewer corrosion in the gas-phase
• No clear effects of temperature for surface pH, sulfate and corrosion loss.
• Model determined to predict corrosion rates based on H2S, humidity and temperature
MANUSCRIPT
ACCEPTED ACCEPTED MANUSCRIPT
Supplementary Information
Title: Determining the long-term effects of H2S concentration, relative humidity and air temperature on concrete sewer corrosion
Authors: Guangming Jiang, Jurg Keller, Philip L. Bond
Tables: 2
Graphs: 2
MANUSCRIPT
ACCEPTED ACCEPTED MANUSCRIPT
Figure SI-1. Trees for the corrosion rates of gas-phase coupons during their exposure tests between 0-12, 12-24, and 24-45 months (from left to right). The expressions at each branch
node are the splitting factor and the levels. E.g. H2S<2.5 means the corrosion rates can be partitioned into two groups by different H2S levels. The left branch is the data for H2S<2.5 ppm and the right is for H2S >=2.5 ppm. The numbers at the end of each branch are the mean values for the corrosion rates in that group. The analysis shows that H2S and RH are the explanatory factors identified to be responsible for the difference in the corrosion rates.
MANUSCRIPT
ACCEPTED ACCEPTED MANUSCRIPT
Figure SI-2. Trees for the corrosion rates of partially-submerged coupons during their exposure tests between 0-12, 12-24, and 24-45 months (from left to right). The analysis shows that H2S is the key explanatory factors identified to be responsible for the difference in the corrosion rates. It also suggests that RH and temperature may have played a very limited role.
MANUSCRIPT
ACCEPTED ACCEPTED MANUSCRIPT Table SI-1. Analysis of variance (ANOVA) results for the corrosion rates of gas-phase concrete coupons 1.
Corrosion Factors Df Sum of Sq RSS F value Pr(>F) Significance 2 rate
H2S 1 0.1711 23.1080 0.2387 0.6285
0-12 month Humidity 1 3.5094 26.4460 4.8961 0.0342 *
Temperature 1 0.1170 23.0540 0.1633 0.6888
H2S 1 1.3560 5.6309 10.1507 0.0032 **
12-24 month Humidity 1 0.6751 4.9500 5.0538 0.0316 *
Temperature 1 0.0317 4.3065 0.2373 0.6295
H2S 1 1.3873 5.3671 11.1550 0.0021 **
24-45 month Humidity 1 0.8525 4.8324 6.8550 0.0134 *
Temperature 1 0.0050 3.9848 0.0405 0.8418
1 Df stands for degree of freedom; RSS, residual sum of square; Pr(>F), the p-value using the
F-test. MANUSCRIPT 2 Significance codes based on the Pr value: 0-0.001: ***, 0.001-0.01: **, 0.01-0.05: *, 0.05-0.1: ., 0.1-1: NA
ACCEPTED ACCEPTED MANUSCRIPT Table SI-2. Analysis of variance (ANOVA) results for the corrosion rates of partially submerged concrete coupons 1.
Corrosion Factors Df Sum of Sq RSS F value Pr(>F) Significance 2 rate
H2S 1 42.9690 111.0940 20.1840 8.62E-05 *** 0-12 Humidity 1 1.4160 69.5410 0.6652 0.4208 month Temperature 1 3.0720 71.1970 1.4432 0.2384
H2S 1 33.2560 62.5930 35.1418 1.51E-06 *** 12-24 Humidity 1 0.9660 30.3030 1.0206 0.3202 month Temperature 1 3.4320 32.7690 3.6265 0.0662 .
H2S 1 11.9622 21.9740 38.2345 6.39E-07 *** 24-45 Humidity 1 0.4511 10.4630 1.4420 0.2386 month Temperature 1 0.2183 10.2300 0.6978 0.4097
1 Df stands for degree of freedom; RSS, residual sum of square; Pr(>F), the p-value using the
F-test. MANUSCRIPT 2 Significance codes based on the Pr value: 0-0.001: ***, 0.001-0.01: **, 0.01-0.05: *, 0.05-0.1: ., 0.1-1: NA
ACCEPTED